Stereotactic injections of horseradish peroxidase and/or radioactive isotopes are being perfomed in the monkey retina and/or optic nerve to label accruate nerve fiber bundles, corresponding to those most susceptible to glaucomatous damage in man. Once the anatomic location of these bundles has been clarified, including their course through the optic nerve head, alterations induced by changing intraocular pressure will also be studied.